1. Field of the Invention
The present invention relates to a backlight unit which can implement a local dimming function.
2. Description of the Related Art
Liquid crystal display (LCD) devices have a number of advantages. Specifically, LCD devices have a low weight and a small thickness, can be driven with low power, and can implement high resolution. Therefore, cathode-ray tubes are being replaced with LCD devices.
An LCD device includes a backlight unit and a liquid crystal panel. The backlight unit generates light to provide to the liquid crystal panel. The liquid crystal panel displays an image by adjusting the transmittance of the light provided from the backlight unit.
The backlight unit may be divided into a direct type and an edge type depending on the position of a light source. The direct type backlight unit includes a light source disposed under the liquid crystal panel, and the edge type backlight unit includes a light source disposed on a side surface of the liquid crystal panel.
The direct type backlight unit has a structure that can implement a local dimming function. The local dimming function is referred to as a backlight driving method, in which a liquid crystal panel is divided into a plurality of regions, and the luminance value of a light source is adjusted for each divided region in accordance with a gray level corresponding to the divided region. Therefore, when the LCD device has a local dimming function, a high contrast ratio and a clear image can be implemented. Further, since the light source can be driven only for a desired region, it is possible to reduce power consumption.
However, the direct type backlight unit requires higher power consumption than the edge type backlight unit. To secure uniformity of light, the direct type backlight unit should have a sufficient thickness. Therefore, there is a limit in reducing the thickness of the backlight unit, that is, the thickness of the LCD device.
Meanwhile, the edge type backlight unit requires lower power consumption than the direct type backlight unit, and can be manufactured with a small thickness. In the edge type backlight unit, however, although light is partially provided to a light guide plate through a local dimming function, the light is uniformly emitted to the upper portion by the light guide plate. That is, the edge type backlight unit cannot obtain an effect of the local dimming function. For example, the improvement of contrast ratio cannot be achieved.
Therefore, there is a limit in applying the local dimming function to the edge backlight unit.